This invention is directed to high or low pressure gas discharge lamps used for lighting and display.
Gas discharge lamps (mercury vapor, sodium vapor, metal halide) are an important segment of the lighting industry. It is well known that the luminous efficiency of gas discharge bulbs increases substantially at high pressures (1-200 atmospheres). However, the containment of such high pressures in a transparent vessel has presented significant problems. Gas pressure is restricted in many instances because of the difficulty of finding materials that are sufficiently lightweight, while at the same time capable of withstanding high temperatures and pressures. Furthermore, such materials, to be practical, must be capable of relatively inexpensive mass production. The usual construction of gas discharge lamps is to suspend a transparent pressure and heat resistant discharge tube by means of a metal framework within an outer glass bulb. The conventional discharge tube is made by glass blowing techniques in a continuous flow method, i.e., a process in which one lamp is constructed at a time.
The present invention relies on an entirely new paradigm for the construction of high pressure gas discharge lamps. Rather than a discharge tube made by glass blowing using techniques that allow only one lamp to be manufactured at a time, the present invention relies on methods of fabricating high pressure "microlamps" utilizing micromachining techniques which are similar to integrated circuit fabrication techniques such as the etching and bonding of planar substrates. This allows many lamps to be fabricated at once, for example, by batch processing in a wafer. It also allows each lamp to be constructed in exactly the same manner, which allows all lamps to have similar properties and minimizes variations between lamps. The present invention incorporates an improved gas discharge lamp that can withstand very high pressures and the method of making such a lamp by means of integrated circuit manufacturing techniques.
It is a further objective of this invention to make extremely small lamps with features which cannot be achieved by traditional glass blowing methods in a reproducible and cost-effective manner. These features include microlamps with electrodes placed on one end, microlamps with hot-restrike capabilities and microlamps with an integrated device, which makes lamp ignition easier.
The lamp is manufactured from two or more planar sheets of temperature and pressure resistant transparent material. A cavity is etched in one or both of the sheets and electrodes are deposited in the cavity. The cavity is charged with a filler appropriate to the type of lamp being manufactured such as mercury, xenon, argon, sodium or metal halides, or some combination thereof. The sheets are then bonded together so as to seal the cavity within the sheets. Contact may then be made with the electrodes to activate the lamp, by creating an arc within the cavity.
The present invention incorporates a built-in ultraviolet ignition enhancer or starter. A separate "enhancer" cavity may be fabricated in the substrate sheets in close proximity to the lamp cavity. The enhancer cavity may be charged with an appropriate gas, and electrically coupled to the electrodes of the lamp cavity. During ignition, the gas in the enhancer cavity emits ultraviolet light, increasing the photoemission of electrons from the electrode material or the inside wall in the main lamp, thus facilitating the ignition of an arc in the main lamp.
The present invention also provides a hot re-strike capability in the lamp. In particular, two lamps comprised of adjacent cavities in the substrate may be connected to the starting ballast in parallel. An initial starting voltage will create an arc in one of the lamps. Because of the low thermal conductivity of the substrate, the adjacent lamp remains relatively cool. If the arc in the first lamp is extinguished, the adjacent lamp will start immediately upon re-strike. Further, because of the small dimensions of these "microlamps", the source of light looks similar at a distance.
The present invention further provides a method of making single-ended microlamps in which the electrodes are placed on one side of the cavity created within the sheets, rather than on diametrically opposite sides. This configuration allows a reduction in size, improved optical applications by removing shadowing effects present in double-ended lamps, improved start-up and heat dissipation, precise control of the arc gap, and allowing lower wattage high intensity discharge lamps by lowering the thermal mass of the lamp.